Field of the Invention
The present invention generally relates to a powertrain for a hybrid vehicle.
Description of Related Art
A hybrid vehicle, which is driven by electric power and power from an internal combustion engine, is controlled to drive in periods with high system efficiency by an engine and an electric motor, so the entire efficiency is high and an exhaust gas can be significantly reduced, thus such a vehicle has been increasingly used and is representative of a typical environment-friendly vehicle.
The way of splitting power in a hybrid vehicle is composed of a mechanical mechanism that transmits power from an engine directly to an output shaft, using a power split device that splits a power flow such as a planetary gear set and an electric mechanism that operates a generator to generate electricity using power from the engine and charges a battery with the generated power or drives a motor with the energy of the charged battery.
The power split type of hybrid system has an advantage in that it is possible to operate the engine independently from the output and freely turn on/off the engine during driving, and to achieve an electric vehicle mode.
Further, the effect of an electrically variable transmission obtained by two motor generators allows for efficient operation of the engine and the motor has constant output at each speed, so there is essentially no need for a transmission.
However, there is a need for a transmission to ensure low-speed torque at a high maximum speed of a vehicle.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.